1. Field of the Invention
The present invention relates to a complementary metal-oxide-semiconductor (CMOS) image sensor (CIS), and particularly to a CMOS image sensor able to suppress dark leakage and crosstalk, the method of making the same, and the method of the suppression.
2. Description of the Prior Art
CMOS image sensors nowadays are widely applied in digital electrical products. For example, the line CMOS image sensor is predominately applied in the scanners, and the plane CMOS image sensor is predominately applied in the digital camera. Because the standard CMOS transistor manufacturing processes and the recent semiconductor equipments and technologies can be employed to manufacture the CMOS image sensors, the yield of the CMOS image sensor is increasing.
FIG. 1 shows a schematic cross sectional view of a conventional CMOS image sensor. As shown in FIG. 1, a semiconductor substrate 10 is a heavy doped P type substrate (P+ substrate). A lightly doped P type well (P− well) 12 is formed in the semiconductor substrate 10. A plurality of photodiodes 14 are formed in the P type well 12. A shallow trench isolation (STI) 16 with the P type well together acts as an electrically insulating material to prevent short-circuiting due to contact between the photodiodes 14 and other components. The photodiodes 14 is covered with a SiN/SiON multilayer serving as an anti-reflection coating (ARC) 18 for a better response.
However, the formation of the ARC layer and/or the STI often leads Si of the underlying substrate under stress that will increase the risk of junction leakage. Furthermore, under the miniaturization of devices, the distance between the photosensor cell structures is decreased, while the photosensor cell structures are wanted to be as deep as possible for improving the capacity. However, the depth of shallow trench isolation is generally from 3000 to 4000 angstroms which is far not as deep as the desired photosensor cell structures. Moreover, a P type substrate is employed. Therefore, the charges will have a charge life long enough to migrate to an adjacent pixel easily, leading to crosstalk.
Therefore, a novel structure or method is still needed to solve the problems of dark leakage and crosstalk for CMOS image sensors.